In patent application publication GB-A- 2223448 there is disclosed a noise attenuation panel having a backing component part, a facing component part and a cellular component part having a multiplicity of open-ended juxtaposed cells, the backing component part extending across the ends of the cells of the cellular component part at the rear thereof and the facing component part extending across the ends of the cells of the cellular component part at the front thereof. In addition, the facing component part comprises or includes an outer facing sheet which is made of a porous permeable thermoplastics material. Preferably, the porous permeable thermoplastics material is produced by powder sintering of a thermoplastics materials.
In one embodiment of the invention described in GB-A-2223448, the cellular component part comprises a single cellular element having wall portions which extend across the element from the front face thereof to the rear face thereof and which provide bounding surfaces for an array of open-ended juxtaposed cells.
In another embodiment of the invention described in GB-A-2223448, the cellular component part is sub-divided into a front cellular element and a rear cellular element positioned to the rear of the front cellular element with a septum element extending between the two cellular elements. Each cellular element has wall portions which extend across the element from the front face thereof to the rear face thereof and which provide bounding surfaces for an array of open-ended juxtaposed cells.
While the panel disclosed in GB-A-2223448 has been found to be successful for use in aero engine environments, drawbacks may be found in using a cellular component part formed as a single cellular element or as two cellular elements in which the element or each element is formed as described.